It is desired to keep approximately the same amount of tension on the curtain as it is lowered from the completely stored position into the completely dispensed position. Further, it is desired to keep approximately the same amount of tension on the curtain between the storage roller and the driving roller. Constant tension on the curtain between the storage and driving rollers results in the curtain's smooth storage in a small area. Further, and importantly, constant tension between the storage and driving rollers enables use of a smaller and lower powered electric motor. Employing a variable reference point for the spring of the instant invention enables the maintenance of approximately constant tension in the flexible curtain as it traverses between the open and closed positions and between the closed and open positions. By closed it is meant that the curtain covers the opening in the building and by open it is meant that the curtain does not cover the opening in the building. In the closed position the curtain is fully deployed or dispensed from the storage roller and in its open position the curtain is fully stored or wound on the storage roller. Without a variable reference, the driving motor must use more energy as the curtain progresses from the open position toward a closed position. During rewind of the curtain from the closed position to the open position, constant tension between the driving roller enables smooth winding of the flexible curtain of the storage roller.
U.S. Pat. No. 958,605 to Doring discloses a fixed sleeve "c" and a nut "l" having lugs or projections "k." Nut "l" moves leftwardly and rightwardly as it is driven by threaded shaft "g." A curtain is affixed to a roller "a" and the roller is affixed to a toothed gear/hub "b." Gear/hub "b" is rotatable with respect to the fixed sleeve "c." Gear "b" drives gears "d" and "e" which drive gear "f" in the same direction as gear "b." Gear "f" is affixed to shaft "g" which is threaded. Rotation of the roller "a" causes the threaded shaft "g" to rotate through nut "l" causing nut "l" to move leftwardly storing energy in the spring as the curtain is pulled downwardly. The spring is fixed at one end, however, and a variable reference is not employed. Energy stored in the spring is released when the curtain is released from a restraint and it is this energy which returns the curtain to its stored position.
U.S. Pat. No. 2,842,198 to Prieto discloses a split ring torsion regulator which limits expansion and, hence, tension in a spring. The split ring is adjustable but a variable reference is not employed.
U.S. Pat. No. 667,302 to Edwards discloses an apparatus by which the tension of the spring in a roller may be changed or adjusted without the removal of the roller from its brackets or mountings. More specifically, a spring is connected to a roller and to a rotatable part or a spring is connected to a barrel and a rotatable spindle. The rotatable part or the rotatable spindle are adjustable as desired. However, the adjustment is permanent and does not provide a variable reference point for the spring in either instance.
U.S. Pat. No. 1,828,623 to G. M. Sacerdote discloses a pulley driven shaft and a spring connected to its shaft and to a roller. When the screen is unwound from the roller the belts will be wound around the pulleys and vice versa. As the screen and belts are thus wound, the diameter of the roller and pulleys vary and the tension upon the screen is such to keep the curtain taut, varying between two limits which are not far apart.
U.S. Pat. No. 3,955,611 to Coles et al. discloses an awning construction particularly adapted for mounting on a mobile home. The awning includes an awning shade having one end fixed to an outside wall of the mobile home, and the other end of the awning shade is attached to an awning roller, which roller is pivotedly connected to the same outside wall. The awning roller includes an elongated torque rod which is nonrotatably connected to a pair of support arms. The support arms are pivotedly connected to the outside wall. A tube is rotatably mounted on the torque rod and is secured to the other end of the awning shade. A torsion spring connects the torque rod with the tube to rotate the tube relative to the torque rod and holds the tube up against the wall of the mobile home in its normal condition. A lock 126 releasably locks the tube relative to the torque rod to allow the tube to stay selectively in an extended position away from the side wall. See, FIG. 6.
U.S. Pat. No. 4,013,113 to Frei discloses a shutter which includes a curtain formed of elongated bars hinged to one another at longitudinal edges and guided at their ends in laterally spaced guide grooves extending along opposite sides of an opening to be controlled by the shutter. A rotatable member is mounted in an upper receiving zone, such as a lintel above the opening, and the rolling bar curtain is trained about this member for direction reversal during raising and lowering. The laterally spaced guide grooves extend along the peripheral portion of this rotary member and are then branched to form branch guide grooves extending downwardly from the rotatable element into a recess formed in the lintel or the like. Guide elements, such as pins or rollers on the ends of each bar, cooperated with the branch guide means to conjointly guide the bars to form at least one vertical pile of bars superposed in horizontal orientation in the recess, responsive to raising of the curtain. The rotatable element may be circular or may be polygonal and if polygonal, has sides each conforming to the width of a bar of the curtain. This invention is demonstrative of the complexities of guiding and managing a curtain that is somewhat flexible and made from rigid sections.
U.S. Pat. No. 4,478,268 to Palmer discloses a door for closing a vehicular traffic passageway. The door is a curtain fabricated from a hard flexible material. The curtain runs in opposing channels, is mounted on a counterbalanced windup drum and under impact changes weight and moves out of the channels and is wound up to open the vehicular passageway.
U.S. Pat. No. 4,601,320 to Taylor discloses a pressure differential compensating door which includes a curtain for closing a doorway having a first upper end, a second lower end and side edges and a counterbalanced curtain winding mechanism having the first end of the curtain attached thereto for raising and lowering the curtain.
None of the related art, however, solves the problem of maintaining approximately constant tension between the storage roller and the drive roller throughout the travel of the curtain from a fully stored position to a fully deployed position and back. Further, none of the related art solves the problem of maintaining approximately constant tension between the drive roller and the storage roller so as to enable use of a relatively low power motor. Present designs require the use of a large motor so as to overcome the resistance of a spring connected at one end to a storage roller and at the other end to a fixed structure (ground). Present designs require a large motor because the resistance of the spring increases linearly as the curtain extends toward its fully deployed position.